I watched both the DBZ and GT serious. Those of you who haven't watched the GT series, I would definitely recommend it for watch. I don't recommend, however, that you really pay attention to the storyline. It's the battles that are fascinating to watch; they're almost more epic than DBZ's.
Though for some reason, the Cell saga(in DBZ's) seemed to be popular with a lot of people. I do have to admit however, that it is very awesome and had a lot of good parts to it and was dramatic and many people hyped up over it; but...eh. For me, the Cell saga was okay. It never screamed spectacular except in the very end when the saga has really reached it's peak and Gohan and Cell were tied in a Kamehameha.
It was all thanks to Vegeta that cell was dead. Finally, the Price of all Saiyans redeemed himself. But honestly, I found the Majin Buu saga to be sort of more entertaining and whatnot. D: